#include <stdio.h>

double f(int n){
    int i;
    double sum=0;
    for(i=n;i>0;i-=2){
        sum+=1/(double)i;
    }
    return sum;
}

int main(){
    int n;
    printf("Enter an integer: ");
    scanf("%d",&n);
    printf("%lf\n",f(n));
    return 0;
}
